1. Field of the Invention
This invention relates to a stamping-moldable material (hereinafter simply referred to as "stampable material") composed of a thermoplastic resin and capable of producing by stamping molded articles which are required to exhibit a high surface smoothness and heat resistance, no anisotropy in shrinkage on molding, low warping characteristics, excellent mechanical strength and the like for uses such as the exterior parts of automobiles.
2. Discussion of the Background
A method which comprises preheating a thermoplastic resin molding material reinforced with long glass fibers above the melting temperature of the resin and then feeding the preheated material between a pair of molds, followed by rapid pressing to conduct compression molding is called stamping molding or simply stamping. Since this method has such advantages as: being similar to that used to stamp sheet metal; yielding articles having excellent properties such as a lighter weight than sheet metal and resistance to corrosion; high productivity; a solid (monobloc) molding incorporating ribs, bosses, or the like, enabling a reduction in the number of parts; and the like, there is a considerable amount of latent demand for the stamped articles produced by this method for uses including automobile parts, electrical parts, parts for general goods, etc.
There is a known method for preparing molded articles of glass fiber reinforced thermoplastic resin which comprises utilizing a needled glass fiber mat (U.S. Pat. No. 3,664,909). However, this method has several drawbacks. The obtained articles are sometimes insufficiently rigid, thus requiring a high pressure, for example 100 kg/cm.sup.2, for obtaining complex-shaped or deep drawn articles, therefore requiring in turn a high-pressure pressing machine. Further, the obtained molded articles exhibit glass fibers blooming on the surface, thereby causing problems in handling and in surface smoothness and rendering difficult the use of the molded articles in exterior parts directly visible or touched by hand. As to the problems of glass fibers blooming or cracks on the surface, it is known that surface smoothness is improved to some degree by incorporating mica into the stampable material (Japanese Patent Application Kokai No. 120727/1985). However it has been noted that the incorporation of a filler worsens the state of impregnation of a stampable material. Therefore, it has been difficult to, without impairing the mechanical properties of a stamped article, incorporate a filler into a glass fiber mat and resin in an amount sufficient to exhibit an improvement on the surface smoothness and have the resulting composition well impregnated and consolidated.
Thus, there is a need for molded articles of reinforced thermoplastic resins which possess good mechanical properties and a smooth surface. There is a further need for a stampable material comprising a reinforced thermoplastic resin which can give molded articles which exhibit good mechanical properties and a smooth surface. There is yet a further need for a process to produce a stampable material comprising a reinforced thermoplastic resin which can give molded articles possessing high surface smoothness and good mechanical properties.